Engine emission control systems may utilize various exhaust sensors. One example sensor may be a particulate matter sensor, which indicates particulate matter mass and/or concentration in the exhaust gas. In one example, the particulate matter sensor may operate by accumulating particulate matter over time and providing an indication of the degree of accumulation as a measure of exhaust particulate matter levels. The particulate matter sensor may be located upstream and/car downstream of a diesel particulate filler, and may be used to sense particulate matter loading on the particulate filter and diagnose operation of the particulate filter.
One example of a PM sensor is shown by Maeda et. al. in US 20120085146 A1. Therein, the particulate matter sensor is attached to the top of an exhaust pipe and housed within a cylindrical protection tube. The PM sensor additionally includes a sensor element that is positioned closer to a center of the exhaust pipe so that the sensor output more reasonably represents an average soot concentration in the exhaust pipe. In addition, the PM sensor includes inlet apertures configured to direct the exhaust into the sensor and towards the sensor element. Herein, the sensor element is positioned closer to the inlet holes to allow the sensor element to capture more of the incoming particulates.
However, the inventors have recognized potential issues with such sensor configurations. As one example, such an arrangement may make the sensor element more vulnerable to being contaminated by water droplets in the exhaust condensing at or near the inlet apertures. In such sensor configurations, additional protective coating may be required to protect the soot sensor element from direct impingement of larger particulates and wa ter droplets. Adding additional protective layer may reduce the electrostatic attraction between the charged soot particles and the electrodes of the sensor element and may lead to reduced soot sensor sensitivity. With reduced sensitivity, the soot sensor may not be able to determine the leakage of the particulate filter in a reliable way. Thus, errors in the sensor may lead to a false indication of DPF degradation and unwarranted replacement of functioning filters.
On the other hand, if the sensor is mounted at the bottom of the exhaust pipe, as shown by Paterson in U.S. Pat. No. 8,310,249 B2, water condensing at the bottom of the exhaust pipe may overflow into the sensor element thereby contaminating the sensor element. Such contamination of the sensor element may lead to fluctuations in the output of the sensor, thereby decreasing the accuracy of estimating particulate loading on the particulate filter.
The inventors herein have recognized the above issues and identified an approach to at least partly address the issues. In one example approach, a particulate matter sensor assembly comprising a cylindrical assembly, an inner device positioned within an outer device of the cylindrical assembly with a radius less than a radius of the outer device, and a sensor element located above an annular space proximal to a dome located at a top end of the outer device. In this way, by positioning the sensor element above the annular space, issues related to water droplets and larger contaminants impinging on the sensor element and causing fluctuations in the sensor output may be reduced.
As one example, an exhaust particulate matter sensor assembly may be positioned downstream of an exhaust particulate filter in an exhaust pipe. The particulate matter sensor may include a cylindrical assembly including perforations located at a bottom end, and a sensor element positioned at a top end of the assembly, with the inner device located between the two. The cylindrical assembly further includes an interior flow space divided into equal portions via a plurality of dividers, and where each of the divided portions includes at least one perforation of the perforations. A dome is located at the top end of the assembly and extends outside of the exhaust passage.
The perforations fluidly couple the interior flow space to the exhaust passage. As such, exhaust gas flows through the perforations to enter and exit the cylindrical assembly. The inner device is radially smaller than the cylindrical assembly. As such, a small annular space exists between the circumference of the inner device and an inner surface of the outer device. The sensor element is positioned on surfaces of the dividers, with oppositely charged electrodes of the sensor element being located on alternating divider surfaces. By doing this, exhaust gas flows over the sensor element, into the dome where the exhaust gas is scrambled and redirected to different divided portions, and back over the sensor element. This may provide more uniform particulate deposition across surfaces of the sensor element.
In this way, the functioning of the sensor element may be improved and the sensor may be rendered more reliable. In addition, by enabling a more accurate diagnosis of the exhaust particulate filter, exhaust emissions compliance may be improved. This reduces the high warranty costs of replacing functional particulate filters. The exhaust may exit the sensor via the perforations. The symmetrical design of the cylindrical assembly and inner device eliminate manufacture process for specific sensor orientation at the installation and enhance the sensor repeatability.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.